The present invention relates to packing units used in air pollution control equipment, gas and liquid contact apparatus for absorption or desorption of gas, rectification columns, mist and entrainment separation of solid and liquid particulates, and the like.
Packing materials are of various sizes and shapes, usually designed to bring two phases of a system, typically a gas or mist and a liquid, into intimate contact. Filamentous packing materials are disclosed in U.S. Pat. Nos. 2,867,425 and 3,752,453. Other known packing configurations are Berl saddles and Raschig rings.
Packing materials accomplish their purpose either by presenting an extended thin film of one phase, usually the liquid, to the other phase or by constantly renewing the surface of one phase, usually the liquid, so that the most efficient mass transfer between phases can occur with the least expenditure of energy. The surface area of the packing material is therefore an important factor.
Interstitial holdup points are points where the surface of one phase is renewed by agglomeration and redispersion, to provide a fresh unsaturated surface to the other phase. The number of interstitial holdup points provided per cubic foot of packing material is thus extremely important.
Interstitial holdup points are provided both by the shape of the packing material unit and by its intersections with the packing material units (xe2x80x9cpacking unitsxe2x80x9d) immediately surrounding it. Interlocking increases the number of contact points between packing units and therefore increases the number of interstitial holdup points. However, interlocking also has disadvantages, such as the tendency to block fluid flow and thus increase the pressure drop through the packed space, such as a packed column. Interlocking where a packing unit fits within another packing unit is referred to as xe2x80x9cnestingxe2x80x9d and can dramatically block the fluid flow and significantly increase the pressure drop. Extensive interlocking also requires more packing units per cubic foot, thereby increasing the weight and cost, which are particularly significant considerations in large installations.
Interlocking can be prevented, but this usually reduces the number of interstitial holdup points. Therefore, complete prevention of interlocking of prior art packing units may not be desirable. The preferred packing unit would provide a large number of independent interstitial holdup points so that reliance for such holdup points from contact with other packing units by interlocking is lessened, and interlocking can be reduced without significant adverse effect. Such a packing unit would have the capacity to provide better phase surface regeneration even without being interlocked with other packing units and would simultaneously require less pressure drop through the packed space, thus increasing efficiency.
Accordingly one object of the present invention to provide a packing unit for a liquid-gas contact apparatus by which more efficient operation of the apparatus is achieved while using fewer packing units per cubic foot.
Another object of this invention is to provide a packing material unit which provides for less interlocking with other packing units thereby requiring fewer units per cubic foot while simultaneously providing within each packing unit an increase in contact between the gas and liquid phases passing through the apparatus.
A further object of this invention is to provide more independent interstitial holdup points, and thus better phase surface regeneration, in an individual packing unit, thus reducing dependency on contact by the packing unit with surrounding or interlocked packing units to achieve the desired number of holdup points.
Still another object of the present invention is to provide a packing unit which results in the maximum time for mass transfer between the liquid phase and the gas or mist phase by increasing within the unit itself the number of points of surface regeneration.
Yet another object of this invention is a packing unit which provides a longer retention time of the liquid phase passing through a liquid-gas contact apparatus while reducing the pressure drop in the gas phase through the apparatus.
By the present invention, a surface or surfaces of a packing unit are provided with sharply contoured projections which define abrupt interruptions to liquid flow along the surface and which reduce interlocking between adjacent units.
Such projections can be of any number of different structural configurations designed to achieve rapid breaking up of liquid flow contacting the projection either as a result of impact therewith by dropping from a unit thereabove or by contact therewith during flow along the packing unit surface. For example, the projections can be cylindrical, square, rectangular, triangular, chisel pointed, oval shaped, or diamond shaped. It is necessary that the projections or recesses define abrupt changes in the surface contour to cause immediate splitting or breaking of liquid impinging thereagainst to facilitate rapid surface regeneration. Such splitting or breaking of liquid is distinguished from unit surface configurations designed simply to provide a larger surface area and then to spread or guide liquid flow evenly relative to or across that surface area. The present invention is characterized by providing more holdup points and at the same time more positive breaking of liquid flow whereby acceleration of surface regeneration is achieved without the degree of interlocking heretofore required to achieve the desired number of holdup points.
Although applicable to any of the known packing unit configurations, such as the Berl saddles and Raschig rings mentioned above, the present invention is described in conjunction with a filamentous packing unit. Such a filamentous packing unit may be provided in any suitable configuration and is described herein in a preferred form which is a torus having a plurality of loops having internal offsets, an exterior ring, and an interior support. The loops, the exterior ring, and the interior support each have protuberances which provide interstitial holdup points. It will be appreciated that the specific loop configuration described hereinafter is but one of many loop configurations which could be designed without departing from the basic configuration of a plurality of loops having internal offsets and being oriented about a central axis.
In the preferred packing unit configuration, each loop is a filament having a first half in a first plane and a second half in a second plane, the two planes preferably being parallel and slightly offset from each other, so that a loop is not in a single plane, and the two halves conveniently being joined to each other at their open ends. This loop configuration is altered by abrupt internal projections, external projections, and internal connecting projections. The internal connecting projections connect a point on a first half of the loop with a point on the second half of the loop so as to provide a pathway between those points and provide strength to the loop and to the packing unit.
Each loop is connected to first and second adjacent loops, with a first half of the loop being connected by one or more cross bridges to a corresponding first half of a first adjacent loop, and with the second half of the first loop being similarly connected by one or more cross bridges to a corresponding second half of a second adjacent loop. In addition, the cross bridges preferably have projections.
The first and second planes of a loop are mirror planes to the first and second planes of an adjacent loop. That is, the first planes are not parallel to each other and will intersect, and the second planes are not parallel to each other and will intersect.
The external ring has a plurality of first projections which extend radially outward from the ring, and a plurality of second projections which extend coaxially with the ring. The external ring preferably encircles and is connected to the outer open ends of the loop halves.
The interior support is connected to the inner open ends of the loops, has a plurality of interior projections which converge at the axis of the interior support, and has a plurality of exterior projections which extend coaxially with the axis of the interior support and the packing unit.
This configuration effectively reduces nesting or interlocking of packing units, and defines a plurality of holdup points therein. The abrupt changes in the surface contour of the loops and ring of the preferred embodiment advantageously lend to the manufacture of a packing unit which provides numerous small targets for the inertial impactment of liquid or solid particulates from an airstream. A multitude of small targets is well established as providing better efficiency in particulate removal. The preferred embodiment of this invention allows the interstitial or surface renewal points to be maintained for maximum gas absorption or desorption, while obtaining good efficiencies in particulate removal as well. By reducing interlocking and compacting of the units a reduction in pressure drop through a body of packing units is achieved as compared to prior art units which provide the same degree of removal.
This configuration provides substantial strength, such that the packing units can be stacked to large heights and handled with little care without collapsing or distorting. This benefit is provided with little added weight or cost over conventional packing units.